The present invention relates to the transportation of objects such as semiconductor wafers along a track on an air film and more particularly to the minimization of movements of the objects in any direction but the desired direction of transportation.
For some time now objects such as semiconductor wafers have been moved along a track on an air film during manufacturing and testing processes. In the past, the forces exerted by the air film on the wafers has resulted in the wafers contacting with dust or environment control shields covering the track or with the guides placed along the track to constrain the motion of the wafers. This has resulted in damage to the wafers lowering the yield rate of the semiconductor circuits on the wafers. Therefore it is desirable that the need for such guides to correct the motion of the wafers be eliminated or reduced.
The transportation of a wafer on a supporting air film, without boundary guides is difficult because low sliding friction and momentum of the moving wafer causes the wafer to diverge from the desired direction of transportation. A system having such a wafer handling capability must have an air film "structure" with unique control properties. Namely, it must be able to constrain the wafer motion in various directions while allowing controlled motion in a desired direction and manner. Furthermore, these control characteristics must be inherently stable and thus resistive to extraneous effects which could cause motion instabilities.
Ideally, this system also features simple and low cost construction; ease in installation and maintainability; low air consumption; performance insensitivity to clean air enclosures; clean operating environment; and, high overall reliability.